Changed fs.watch to fs.watchFile to resolve issues with Vim on OSX

Changing fs.watch to fs.watchFile resolves an issue with file change detection when using Vim on OS X. 

For more information see this post:
http://www.actionshrimp.com/2012/06/jasmine-node-autotest-with-vim-on-osx/

fixes airportyh/testem#299